From countries suffering social unrest caused by climate change, electing populist leaders proposing to solve the crisis in their borders by expanding their "living space" and so on.

History is a circle...

No, History is not a circle, it never repeats itself because the variables always change. Context matters.

> proposing to solve the crisis in their borders by expanding their "living space"

When you are in a crisis mode you don't have to time to wait for elections, the most likely result of social unrest is civil war. There are ample examples in very recent History.

From places with hungry people and newly-arid landscapes. What do you think will happen when they can't get visas? Just happily sit there and starve?

I have a hard time picturing how tired and hungry people would suddenly become a threat against countries producing all the weapons in the world and armed to the teeth. But surely you can explain?

China, as noted by others, stands to lose a lot of arable land and makes plenty of weaponry. India and Pakistan are both likely to become more or less uninhabitable, and have nukes and (for the former) no shortage of people to draft. The United States of America, under a 4C rise, would also see large regions become uninhabitable, and has a northerly neighbour that could not repel an invasion. Russia has already shown a fondness for acquiring territory (see Crimea) when the opportunity presents itself, and Europe is weakly defended.

Not to mention that "set up turrets on the southern border and mow them down" is not the most humane way to handle this, especially since the nations likely to fare OK(ish) are generally the ones that caused this trouble in the first place.

OK, maybe central Africa is not going to be a major military threat.

How about China and India, whose southern parts are densely populated, and who are capable of launching rockets to space, have nuclear weapons for a long time, etc?

You don't want them to feel desperate.

China and India are not desperate enough to choose to reduce their projected increase in coal-fired power stations. Nuke themselves?

No, the idea is:

1) Keep building coal stations

2) Invade northerly regions that are now better for growing crops

Not just China and India. Russia could just about do this for the lolz when you consider they're already expansionist.

Mind you I'm not _endorsing_ this, I'm just worried about it.

> Russia could just about do this for the lolz when you consider they're already expansionist.

In all seriousness if you really want to picture Russia as expansionist, the only time when this was really true was post-WW2 and Cold-war Era. Now Russia is far from being a fool enough to "invade" countries around much beyond their border. Let's not forget NATO as well. I'm not sure in what world this scenario would ever happen.